of the Fishery Board for Scotland. 



373 



from the spawning area where they were shed ; and the eggs of cod and 

 haddock may travel in a similar direction from 20 to 40 miles before 

 they hatch. On the other hand, the floating eggs of the summer spawn- 

 ing fishes will be carried much shorter distances, in some cases only a 

 few miles ; for, besides the higher temperature of the water at that sea- 

 son, the eggs of such species are frequently small, and therefore prone to 

 hatch rapidly. In agreement with these conditions it is also found that 

 the summer spawning species, and notably the flounder and the sprat, 

 shed their eggs much closer to the shore, and within the territorial 

 waters, than those which spawn earlier in the year, for owing to the 

 fact that hatching occurs rapidly, they are not exposed to the same 

 risks of being stranded and destroyed. The gurnard at first sight 

 appears to be, in one respect an exception, inasmuch as its egg is 

 relatively large, and it spawns in the Firth of Forth as well as outside 

 in the offshore waters. Eat it does not spawn in the inshore area until 

 comparatively late, when the temperature of the surface water is over 

 50° F., and the egg would then hatch in about a week. This fish, 

 indeed, reverses the procedure of most sea fishes by migrating in summer 

 to the inshore waters in considerable numbers to spawn, leaving them 

 again in the autumn. Looking over the * Garland's ' trawling records for 

 a series of years it will be found that gurnards are not taken in the trawl 

 in any year, even at the stations east of the Isle of May, until April, and 

 then in small numbers, and with very rare exceptions after October; 

 they are most numerous from the end of May to the end of August. 



It has been already explained that the larval fish, after it has issued from 

 the egg, is almost or quite as inert as it was while still within it, so far 

 as its transport by currents is concerned. But the available information 

 respecting the duration of this period and the earlier part of the post- 

 larval stage, when the yolk sac has been absorbed, is imperfect. It is 

 probably in all cases, and in some cases certainly, much longer than 

 the period spent within the egg. Dannevig (see page 187) has 

 shown that the larvae of plaice from eggs which hatched in thirteen 

 days at the beginning of May, had absorbed the yolk, and entered the 

 post-larval stage eight days after hatching ; while other thirty-four days, 

 or forty-two days from the date of hatching, elapsed before their trans- 

 formation was sufficiently advauced to enable them to remain perman- 

 ently on the bottom. During at least half of this period the post-larval 

 plaice in the sea w r ould be subjected to a considerable extent to the 

 movement of the water around them, and combining this with the 

 movement of the egg, and making allowance for the probably diminished 

 rate of the current in the bottom layers to which the larvae descend, it 

 is a moderate estimate to assume that the young plaice which abound 

 on the sandy beaches, say, in St Andrews Bay, may be from 60 to 

 100 miles south of the place where the eggs from which they w T ere 

 derived were spawned. The duration of the larval stages of other species 

 has been somewhat variously stated by different observers, or not stated 

 at all. It appears to vary from three or four days to ten or twelve 

 days according to the species and the temperature. It is known that 

 an increasing temperature accelerates, and a decrease of temperature 

 retards the absorption of the yolk and the growth of the young fish, 

 just as it hastens or delays the development of the embryo within the 

 eggs. Hence the duration of the larval and post-larval stages of sum- 

 mer-spawning species — and consequently the length of exposure to the 

 influence of currents — is comparatively brief. Very little definite infor- 

 mation exists respecting the length of the post-larval stage except in the 

 plaice. 



